[clang] [CIR][X86] Implement xsave/xrstor builtins Fixes part of #167752 (PR #170877)

[Andy Kaylor via cfe-commits]

https://github.com/andykaylor commented:

Thanks for the PR! This looks pretty good. I just have one minor suggestion and a request for improving the test.

https://github.com/llvm/llvm-project/pull/170877